Experimental investigations of turbulent temperature fluctuations and phase angles in ASDEX Upgrade.

A complete experimental understanding of the turbulent fluctuations in tokamak plasmas is essential for providing confidence in the extrapolation of heat transport models to future experimental devices and reactors.~~Guided by~``predict first'' nonlinear gyrokinetic simulations with the GENE code, two new turbulence diagnostics were~designed and have been installed on ASDEX Upgrade (AUG) to probe the fundamentals of ion-scale turbulent electron heat transport.~ The first, a 30-channel correlation ECE (CECE) radiometer, measures radial profiles (0.5 \textless r/a \textless 0.8) of low-k (ktheta rhos \textless 0.3) temperature fluctuations as well as frequency spectra and radial correlation lengths in unprecedented detail in both L- and H-mode. Typical L-mode levels are in the range 0.3 -- 0.8{\%}. The second is formed by the addition of a reflectometer on the same line of sight to enable measurements of the phase angle between turbulent density and temperature fluctuations. Design predictions are followed by a more traditional ``post-diction'' validation study with GENE. Using a cutting edge synthetic diagnostic GENE shows a factor 1.6 - 2 over-prediction of the fluctuation amplitude, while matching both ion and electron heat fluxes within experimental error.~Detailed sensitivity scans are underway to understand the robustness of this disagreement and a detailed assessment of the experimental errors has been carried out. The discrepancy opens questions about the~role of multi-scale turbulence~physics, but also indicates the need for the comparison of more experimental turbulence properties to have a more complete validation hierarchy. In an effort to understand the discrepancy, \textit{predictions} of~the nT-phase and the radial correlation length have been made along with an assessment of their sensitivity to experimental errors. Comparison to experimental measurements will be discussed.